Aromatic polycarbonates belong to the group of industrial thermoplastics. They are characterized by the combination of the technologically important properties transparency, thermal stability and toughness.
In order to obtain high molecular weight linear polycarbonates by the phase interface process, alkali metal salts of bisphenols are reacted with phosgene in a two-phase mixture. The molecular weight may be controlled by the amount of monophenols, such as for example phenol or tert.-butylphenol. In these reactions practically exclusively linear polymers are formed. This may be confirmed by terminal group analysis.
For the production of linear polycarbonates by the phase interface process reference may be made for example to H. Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol. 9, Interscience Publishers, New York 1964 p. 33 ff and to Polymer Reviews, Vol. 10, “Condensation Polymers by Interfacial and Solution Methods”, Paul W. Morgan, Interscience Publishers, New York 1965, Chapter VIII, p. 325.
In U.S. Pat. No. 4,185,009, DE A 25 00 092 and JP B 79039040 a process is described in which, starting from mixtures of special bisphenols with chain terminators and isatin bisphenols as branching agents, branched, high molecular weight polycarbonates may be obtained by reaction with phosgene in a phase interface reaction. Copolycarbonates with improved flowability based on bisphenol A and bisphenol TMC with isatin biscresol as branching agent are described in DE A 42 40 313.
In DE A 19913533 highly branched polycarbonates are described, in the production of which there are used oligomeric or polymeric branching agents. Branched polycarbonates are disclosed in DE A 19 943 642, which on account of their intrinsic viscosity are suitable for use as material for water bottles.
Thus, U.S. Pat. No. 5,367,044 describes bottles made of branched polycarbonate in which 1,1,1-tris-(4-hydroxyphenyl)ethane (THPE) is used as branching agent in amounts of 0.28 mole % to 0.36 mole %.
On account of their better flowability compared to linear polycarbonates, branched polycarbonates are particularly useful for applications in which a good flow of the polymer melt at relatively high shear rates is desirable, i.e. for example in the injection molding of complex structures. Branched polycarbonates are characterized by their intrinsic viscosity and are no longer regarded as Newtonian fluids.
The branched polycarbonates previously described in the prior art and their production processes are however unsatisfactory as regards their production or have the disadvantage that the attainable degrees of branching are limited. The use of branching agents leads, above a certain concentration, to gelling, which is manifested in the occurrence of undesirable gel particles. Highly branched polycarbonates cannot be obtained at all with the current branching agents since the reaction batch can no longer be stirred if relatively high concentrations of branching agents are used. A highly viscous agglomerate is formed, which is also referred to as a jelly.